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SideshowRob
11-30-2005, 08:44 AM
Here's a topic that's been thrown around by a friend of mine recently. Boat Hull's- smooth or stippled (not sure if that's the correct term)? I hadn't heard of this until just recently, but now I'm curious. An arguement can be made for each; obviously a smooth waxed hull will pass over/ through the water creating as little amount of friction as possible. Now with stippled or "pebbled" hull, automatically you think, no way that will work, or will it? Will that stippling cause the water to froth, also reducing friction against the hull? Is this even worth arguing about? has anyone tested it out?
I'm curious.

(All of our snow melted last night.... Great now I have a second chance to not rake the lawn :boggled: )

txtaz
11-30-2005, 09:31 AM
Rob, I think you mean stepped hulls. They are used on larger offshore type boats. I haven't heard or seen any on smaller boats. They are most likely not needed since not much of the boat is in the water at speed. NOW a big boat has lots of hull in the water and the step will break the friction of hull to water by creating a turbulance.
Some pro's here will know more.
Hope this helps.
Da Taz<<<--- Anyone, DID I get close???

Carl C
11-30-2005, 09:33 AM
A waxed hull creates surface tension which "glues" the boat to the water. I learned driving outboards to never wax the bottom and leave the gearcase in unsanded primer. I think a stepped hull also breaks up surface tension. As for "pebbling" the surface, I've never heard of that.

glashole
11-30-2005, 10:02 AM
not to get off topic but doesn't Regal have a stepped hull in a smaller bowrider??

Carl C
11-30-2005, 10:18 AM
not to get off topic but doesn't Regal have a stepped hull in a smaller bowrider?? I've seen many smaller boats with stepped hulls now. I guess it adds 2 or 3 MPH but I wonder if it adversely affects handling. There's nothing like the way a 22C banks in a tight turn. I think maybe a stepped hull might wreck that.

Lenny
11-30-2005, 10:23 AM
I have heard of stippled hulls before. I used to see them when I was running sailboats years ago. Keep in mind a sailboat, when heeled hard, has a LOT of wetted surface being sucked through the water. Freighters with the "bulbous" bow have a similar phenon going on as they create a large areated bubble to release surface tension alongside the hull as it passes through the water. I have even seena 17' Montauk Boston Whaler with this stipple effect, but I attribute this one to being left in the water for a prolonged period and a terrible resin/lay-up job at the factory.

I have never seen it used on a pleasure/race powerboat yet but I am sure it has been tried. Keep in mind, there is not supposed to be much boat in the water if it is running well anyway.

boxy
11-30-2005, 10:24 AM
Here's a topic that's been thrown around by a friend of mine recently. Boat Hull's- smooth or stippled (not sure if that's the correct term)? I hadn't heard of this until just recently, but now I'm curious. An arguement can be made for each; obviously a smooth waxed hull will pass over/ through the water creating as little amount of friction as possible. Now with stippled or "pebbled" hull, automatically you think, no way that will work, or will it? Will that stippling cause the water to froth, also reducing friction against the hull? Is this even worth arguing about? has anyone tested it out?
I'm curious.
(All of our snow melted last night.... Great now I have a second chance to not rake the lawn :boggled: )

The America's Cup boats were using some sort of pebble technology, and I think our resident Naval Architect did some reaserch into it ...... :D
Do a search, use the keywords CDMA, rivulets, and speed..... :D :D

SideshowRob
11-30-2005, 11:24 AM
I am quite aware of stepped hulls, I used to sell Regals, and in doing so, got to know the use of stepped hulls and there use on larger offshore boats. Some good points were made here. Thank you though to those that recognized that I am not that poor of a speller. I am still curious about this theory, but I will begin by rhino-lining my buddy's hull before anymore research is done. I think he's out of town till Monday :biggrin:

mattyboy
11-30-2005, 11:30 AM
you know I saw a guy at the ramp this summer couldn't figure out what he was doing, I said to myself why would someone with a roller trailer unhook the boat and back down sending the boat onto the stone ramp???
so he was pebbling is hull :p :) ;)

SideshowRob
11-30-2005, 12:18 PM
Funny you should say that Matt. I saw a guy do that in Killarney a few years ago. I also couldn't figure out why he would unhook the boat, then back down the ramp. It made a bad noise when the outdrive hit the concrete. It scared his buddy too, who was sitting in the boat. I almost felt bad watching them try to winch a 2500lb boat back onto the trailer, I imagine the other 60 or so people who were there too, felt the same way.

boxy
11-30-2005, 01:01 PM
Rob here is an analogy that you and maybe 6 or 8 other guys on the site might get.
A curling rock will not travel very far on a sheet of flat ice, put a "pebble" on it, and the rock will travel with very little effort.... :canada: :beer:

turbo2256
11-30-2005, 01:17 PM
The golf ball effect. Sharky of Sarky marine might know some or http://www.boatdesign.net <---- ask the ? here.

SideshowRob
11-30-2005, 04:21 PM
Now ya see Boxy that just makes good sense. And although the rocks do move easily I find it quite difficult manouvering out there. I'm not saying the Molson X has anything to do with it :beer:

gcarter
11-30-2005, 05:44 PM
Rob, I think you mean stepped hulls. They are used on larger offshore type boats. I haven't heard or seen any on smaller boats. They are most likely not needed since not much of the boat is in the water at speed. NOW a big boat has lots of hull in the water and the step will break the friction of hull to water by creating a turbulance.
Some pro's here will know more.
Hope this helps.
Da Taz<<<--- Anyone, DID I get close???
Steps are additional leading edges. Lift is only created on a leading edge, so the more the merrier. I have a pic of a patent drawing from about 1915 showing about 10-15 of them!!!!
Just kidding, there's a limit to anything. But those leading edges have to be ventilated, and that's hard to do. If the side vent gets covered from a wave, that lift turns into suction, and can ruin your day.
ANYTHING that can reduce or eliminate surface tension will reduce drag, so all kinds of things can work.

MOP
11-30-2005, 07:25 PM
On sail boats I know for a fact that a stippled surface is faster, those of you that watched Jim Conners win the Americas Cup in Australia also know that they pulled the boat and applied the plastic Boeing Rivulet coating to the hull. He later said it increased speed by .2 of a knot, that is a very small margin but it did give us the win. The rivulets have be applied to aircraft surfaces for a decent gain in speed allowing for better economy. On KC135' tankers there are spoilers on the lifting surface that have the same effect.
Some of you know I was an avid sail boat racer, after seeing Conners win and reading more about rivulets I gave up my smooth as a babies ass bottom wet sanded down to 600 smooth. The next season I rolled my bottom paint on and did see an increase and yes it was enough to edge out former hard competitors. Not bragging but if any of you make it to Block Island take a look at the Block Island trophy at the library, I aced the 1989 race won over all, I beat all classes on corrected time and also beat the 4 time champ. Got a nice write up in Soundings.
Mad Poodle brought up sanding the bottoms of our boats which I did the aft section, not sure how much it helped but I know it works!
I think the real trick would be to apply the stipple that is on a golf balls surface, the increase in speed over a smooth ball is astounding. I have to think a golf ball flies faster then or Donzi's!

Its all about breaking the stiction layer, smooth is pretty but not as fast!

Phil

pmreed
11-30-2005, 07:58 PM
Punch a bunch of little holes in the bottom of the hull. Attach'em to a manifold and pump air through'em. You only need them in that part of the hull that will be in the water at high speed. That's ventilating, baby!! I have no doubt that such a system would be very effective.

Phil

gcarter
11-30-2005, 08:22 PM
Phil, Dr. Lindsey Lord tried this in the late 40's. He couldn't get air in fast enough. It seems everyone underestimates the amount of vacuum generated under the hull. He also tried ventilating steps from inside the hull, he still couldn't keep up.
Actually, along with your theory, all you have to do is open the holes, the vacuum does the rest.
He also tried venting engine exhaust through the hull bottom, and actually got a supercharging effect far beyond what you get from a good set of headers.

MOP
11-30-2005, 08:31 PM
Awhile back George Carter sent me a diagram of an exhaust system that vented through the bottom a couple of feet ahead of the transom, the design proved to give the particular vessel a boost in speed. Reading this post has me thinking it probably also helped to break the stiction layer aft which also helped a bit.

Phil

MOP
11-30-2005, 08:34 PM
Qoute: George! He also tried venting engine exhaust through the hull bottom, and actually got a supercharging effect far beyond what you get from a good set of headers.
See what I get for watching "LOST" you beat me to the exhaust thing!!!

Phil

mattyboy
11-30-2005, 09:46 PM
pebbles in the hull is one thing
rocks in the head is a whole nother story ;) :p

gcarter
12-01-2005, 07:20 AM
For those who don't know, Lindsy Lord was the inventor of the deep vee hull. His primary work was in patrol boats and fast cargo carriers in the 80'-100' range in the late 40's.
C. Raymond Hunt took the work of Lord, increased the deadrise from about 20* to about 24* and changed the sharp keel of Lord to a round keel.
Almost everything we know about these hulls we love so much was developed by these two men.
While the exhaust idea is real, it wouldn't work for ocean racers because they spend so much time out of water and the effect would be lost.

SideshowRob
12-01-2005, 10:23 AM
So this means we can actually thank the Lord for creating our boats.
You hear actors and football players do it, but now I can do it too, with authority. I like it!

Rootsy
12-01-2005, 11:10 AM
hmmm so what about an area on the running surface with a series of small mini notches that don't pack air from the outside... you'd end up causing many small vacuum pockets behind the edge of the cut as the water flowed over it at speed ... whether this would stick you to the water or break it loose i am not quite sure but bout the first air you got you'd have air trapped to an extent... plus water flowing off of the sharp edge would go turbulant.. i'm speaking only from the keel to say the inner strake.. maybe an inch deep... steep angle less than 90* to running surface and a shallow leadout at maybe 10* to running surface... like a sawtooth pattern... running from the transom maybe 4 feet fore... something like this...

gcarter
12-01-2005, 11:49 AM
Jamie, that may be an idea for a towed model.

turbo2256
12-01-2005, 01:15 PM
I would think the water running into the prop might be disturbed in this model and loose bite as well as the hull. The stepped boats dont ride on the steps at speed they are there to get the hull up on the running surface easier. Often that area has a strake to either side of it to help with stability at speed. Example Checkmate a few years back widened that area for better stability. The notched transom in that area helps and allows a higher "X" dimension and some natural bow lift..

gcarter
12-01-2005, 02:59 PM
I would think the water running into the prop might be disturbed in this model and loose bite as well as the hull. The stepped boats dont ride on the steps at speed they are there to get the hull up on the running surface easier. Often that area has a strake to either side of it to help with stability at speed. Example Checkmate a few years back widened that area for better stability. The notched transom in that area helps and allows a higher "X" dimension and some natural bow lift..
This year at the Sarasota Homecoming, we were led (sort of) to lunch by a 38ZR with shorties.
I got right behind him thinking that in the rough conditions that day it would help me in my MUCH shorter boat.
NOT SO!!!!
The water coming from his transom was so aerated (quite visibly in fact) I had to move out of the way. I have to imagine the props used on the ZR are chosen to accomodate this condition, much like an Arnison.

Carl C
12-01-2005, 04:09 PM
It seems to me that anything more than a slight roughening of the surface such as by sanding would cause more drag rather than less. You can't change a V-hull into an air entrapment hull. Also, steps do more than just aid planing. Stepped hulls have higher top end.

turbo2256
12-02-2005, 06:15 AM
This year at the Sarasota Homecoming, we were led (sort of) to lunch by a 38ZR with shorties.
I got right behind him thinking that in the rough conditions that day it would help me in my MUCH shorter boat.
NOT SO!!!!
The water coming from his transom was so aerated (quite visibly in fact) I had to move out of the way. I have to imagine the props used on the ZR are chosen to accomodate this condition, much like an Arnison.

I am refering to water into the prop not out of the prop